Have only handled the S&W and shot a friend's at the range a little bit, it's a good pistol with a decent trigger but a bit heavy.
The Mark IV Rugers are getting a reputation for crappy triggers. Mine was horrible - heavy, long and gritty. It needed a Volquartsen accurizing kit to clean it up which added a hundred bucks or more to the price, but now that the trigger is good it's a great pistol; reliable, accurate and easy to clean. As a plus, if you ever wanted to get a different model you can find different uppers for sale at a lot lower price than a new pistol and switch back and forth in a few seconds.
Had a total of one Buck Mark but can't find anything negative to say about it - it was accurate and had a good trigger. It never had reliability issues but it was only fed good CCI ammo, no bulk junk, and again, sample of one.
As much as I like my Rugers the Browning will probably check the most boxes right out of the box.
Generally guys that really like Rugers, prefer them over the Browning and vise versa. This is an age old debate because guys are always arguing about which one is the best. Personal experience from when I was a kid is still engrained in my memory banks, from the Buckmark my dad always shot. It malfunctioned all the time. However he did not like to take it apart and clean it.
When I became old enough, I always had a Ruger mk2 pistol of some sort. Whether it be a govt. model, slab side, target, or the standard model. One thing I can say about the Ruger is it functions without hiccup, even when it has not been cleaned in a while. There are guys that say the Ruger is a PITA to take apart and clean. The other day I had my girlfriend time me to see how long it took to clean each pistol. A Ruger MK2 stainless heavy barrel target model and my dad's old Buckmark.
The Ruger requires no tools for disassembly. The Browning required a screwdriver. The Ruger took 2 minutes and 38 seconds to clean. The Browning took 9 minutes and 45 seconds to clean. Had I been in the field and not had a screwdriver, the browning would be left dirty and functioning like crap. Because as soon as it gets dirty, it starts having issues.
As for the triggers. Ruger had a very good reputation for a nice smooth trigger in the Mk2's, then by the time the MK4's came along you start hearing about how bad the Ruger triggers are. This is some of the reason I, and several club members, always recommend a MK2. Because guys tend to badmouth the Ruger triggers, I checked mine the other day and it was 2 1/4 pounds and very consistent. Then I checked my slab side, that is still like new. Pull weight measured 2.5 pounds on that one and very smooth. I had always heard the Browning trigger is better. I checked my dad's old Browning and it weighed right at 2 1/4 pounds as well. All triggers tested are very nice. No negatives that I saw.
Through accuracy testing, the Browning hangs right in there with the Mk2's. After a complete teardown and cleaning, the Browning functioned almost flawlessly. As it did have 3 ftf out of 100 rounds fired. The Ruger had no issues and digested 200 rounds that day.
With this being said, I saw a very nice stainless Browning Buckmark at the LGS the other day. Between that and the Ruger MK4, I would probably also choose the Browning. However, the older MK2 would be the one I'd buy, if all 3 were in the same display case. However, some guys have a propensity against buying used, and somehow think a brand new rifle or pistol is better. Most times they are not.